Origin of and use of PERFIN stamps
The word "perfin" is made up from the first parts of two seperate words 'PERForated INitials'
and is a pattern of tiny holes punched through a postage stamp. Organizations
used perforating machines to make perforations forming letters or designs
in postage stamps they purchased, often in bulk, with the purpose of discouraging pilferage.
The size and number of perfin holes, and sometimes the design permitted, is usually regulated by
law or postal regulation in the relevant country.
They are also sometimes used in a fiscal (non-postal) capacity as a method of assigning payment.

Thanks goes to Peter Maybury for allowing me to reproduce the The Mauritius Fire Insurance Company document, and supplying some examples
of the perfins.

The most common perfins seen are (B) , (BB/&Co.) and (MCB/M)
The stamps were sometimes folded in two's, three's or more and
punched in one go, this produced perfins that are 'upside down' or 'back to front',
but how does this explain the "MCB" 10c pair, see below.

METER cancellations
Meter cancellations are printed by a machine at the offices of the company concerned, as required directly onto the
letters (in red), a solgan may also be included. As meter machines were introduced, the perfin stamps were phased out.
Note all the meter frankings can be clicked on to show the full envelopes.

Two specimen cards showing meter cancellations, the caption on the first specimem indicates it was used from the 1st August,
but the first franking machine was not used until 20th August 1953 (Ibbotson, 1991.)

An ancestor of Barclays Bank, National Bank of South Africa, first entered Mauritius in 1919.
Since then, Barclays Bank Mauritius has grown to be the third largest bank in Mauritius,
after Mauritius Commercial Bank and State Bank of Mauritius, with 20 branches and a market
share of about 10-12%. In 2002, Barclays Bank Mauritius bought Banque Nationale de Paris Intercontinentale (BNPI).
This acquisition brought with it 6 branches to add to Barclays' existing 13 branches.

(click image for larger copy)

Note the large 50c green stamp has 2 pins missing from the B The damage started with this issue,
first with one pin, until the entire top half was missing.

Blyth Brothers and Company is one of the oldest trading companies operating in Mauritius.
It was founded in 1830 and is located in Port Louis. In 1972 it merged with Ireland Fraser & Co. Ltd,
another Mauritius company, to form Ireland Blyth Ltd (IBL).
Today Blyth Brothers functions primarily as a shipping agent.

Established, since 1830, in Port Louis, the company's activities consisted of commerce,
import-export, and insurances and also of loans supplies to planters.
It now (2008) has 39 subsidiary companies in four countries.

The Mauritius Commercial Bank was founded in 1838. It is the largest bank in the country and is
headquartered in Port Louis, the capital of Mauritius. It appears that MCB put its surplus
perfinned stamps into store at the end of 1935. These were drawn out and used during the
second world war when there was a stamp shortage.

The Mauritius Fire Insurance Company was founded from local funds in 1854,
and 17 years later of the Colonial Fire Insurance Company Limited.
Swan Insurance Company was incorporated in March 1955 to take over the activities of Mauritius Fire and Colonial Fire.

Policy document from 1936showing fiscal use of stamps(click image for larger copy)

Possibily stands for (but no proof, i.e. covers with company name etc)
ROBERT LE MAIRE LIMITED was founded in 1931 by Mr. Robert Le Maire who was a Sugar Mill Chemist.
In the 30's, Robert Le Maire Limited was an Import / Export Company involved in the sales of
Standard Vanguard cars, Bearings and plenty other material for Sugar Mills (Starters, Electric Motors, Pumps etc..).
The Company was also exporting Scrap Metal to the U.K. by using its own Shipping Line.
The Electrical and Mechanical Division has since been very diversified and offers now various
equipment for the sugar industry and the crushing plants. It is in the 50's that Robert Le Maire Limited
took over the Massey-Ferguson agency for the sales of tractors in Mauritius.